1. Field of the Invention
The present invention is directed to a method and apparatus which permit a power supervisor in a multi-card modular electronic system to turn on or off power to a given modular processor card based upon considerations of the power needed by the card and the power resources available to the modular electronic system.
2. The Background Art
Multi-card modular electronic systems are common in the computer industry. Typically such systems comprise a back plane having a plurality of connectors to which a number of line cards or processor cards are connected. Processor cards may perform any of a number of functions as well known to those of ordinary skill in the art. The back plane provides electrical interconnections to the processor cards, such as data, power, ground and signalling. Such systems usually include at least one supervisor module which may be on one of the processor cards or may be permanently connected to the back plane. Supervisor modules are commonly used to detect errors and report conditions to a user.
It is desirable to build modular systems which provide for future expansion while providing a relatively low entry cost. In systems employing processor cards which consume significant quantities of power, such as those embodying one or more microprocessors, or equivalently power hungry devices, it may be desirable to provide for modular power supplies which may be added or changed as power requirements increase with the addition of is more processor cards or the substitution of higher power consumption processor cards for lower power consumption processor cards.
In such systems, it is frequently a problem that an individual responsible for such systems may inadvertently place too high a power demand upon a particular power supply configuration of such a system through the addition of a particular processor card to a previously functioning system. The consequences can vary from a simple shut down or an inability to start up to equipment damage. Accordingly, it would be desirable to provide a method and apparatus which could simply protect such systems from the consequences of errors made by inadvertently overlooking available power supply resources in such modular electronic systems.
As back plane conductor lines are a relatively scarce and expensive resource in such systems, it would also be desirable to implement such method and apparatus in a manner which makes a minimum use of such scarce resources.
SUMMARY OF THE INVENTION
Each modular processor card of a modular electronic system carries a component defining its maximum current or power requirements. The component, which may be a resistor, capacitor, serial access memory, or the like, is accessible over a single conductor through a backplane by a power supervisor. The supervisor will determine the current/power requirements of a processor card while the card is substantially powered off. The supervisor may then weigh existing power supply resources of the modular electronic system with existing current/power demand and make a decision to allow power-up of the card if sufficient overhead is available, or, alternatively, make a decision to deny power-up of the card if insufficient additional current/power resources are available. An optional message indicating the outcome of the decision can be transmitted to a user. If the supervisor elects to power up the card, a signal sent on the conductor connecting the card to the supervisor may be used to authorize the card to power up and control circuitry to effect the power up.